RecyclerView下拉重新整理實現

實現分析：
1.通過topMargin實現
2.通過改變頭部高度實現
這裡介紹的使用 第二種方法實現：通過滑動監聽動態的改變頭部高度實現。

1.初始化相關引數

protected void onLayout(boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);
        if (!load) {
            //滑動最大高度
            scroll_height = getHeight() / 3
 
;
            //頭部的高度
            viewHolder_height = getHeight() / 5;
            //得到頭部
            viewHolder = (ViewGroup) getChildAt(0);
            //頭部佈局引數
            params = (ViewGroup.LayoutParams) viewHolder.getLayoutParams();
            params.height = 0;
            viewHolder.setLayoutParams(params
 
);

            //頭部 重新整理文字
            textView = (TextView) viewHolder.findViewById(R.id.textView);
            textView.setText("測試。。。。");
            //得到下拉重新整理控制元件
            rv = (RecyclerView) getChildAt(1);
            rv.setOnTouchListener(this);
            load = true;
        }
    }

2.RecyclerView滑動監聽

/*
        處理RecyclerView觸控事件；
     */
    @Override
    public boolean onTouch(View v, MotionEvent event) {
        if (current_Status == START_REFRESHING) {
            //正在重新整理時遮蔽狀態
            return true;
        }
        startDown();
        if (start_Drop_Down) {
            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    down_Y = event.getRawY();
                    break;
                case MotionEvent.ACTION_MOVE:
                    float move_Y = event.getRawY();
                    //判斷是否下拉
                    float difference = move_Y - down_Y;
                    //difference>0：下滑，difference<=0表示上滑

                    if (difference <= 0) {
                        params.height = 0;
                        viewHolder.setLayoutParams(params);
                        return false;
                    }
                    //不是正在重新整理
                    if (current_Status != START_REFRESHING) {
                        //達到頭部一半就表示達到重新整理條件
                        if (params.height >= viewHolder_height / 2) {
                            //達到下拉重新整理要求的狀態
                            current_Status = STATE_REFRESHING;
                            //更新文字
                            textView.setText("放手重新整理。。。");
                        } else {
                            //重新整理結束狀態（包括重新整理完和未達到重新整理要求）
                            current_Status = STATE_DROP_DOWN;
                            //更新文字
                            textView.setText("下拉重新整理。。。");
                        }
                        params.height = (int) (difference / 3);
                        if (params.height >= scroll_height) {
                            params.height = scroll_height;
                        }
                        viewHolder.setLayoutParams(params);
                    }

                    break;
                case MotionEvent.ACTION_UP:
                    if (params.height >= viewHolder_height / 2) {
                        current_Status = STATE_REFRESHING;
                    } else {
                        current_Status = STATE_DROP_DOWN;
                    }
                    if (current_Status == STATE_REFRESHING) {
                        //執行下拉重新整理
                        new HeadOperation().execute();
                    } else if (current_Status == STATE_DROP_DOWN) {
                        current_Status = END_REFRESHING;
                        //執行下拉重新整理結束後的操作
                        new HeadOperation().execute();
                    }
                    break;
            }
            if (current_Status == STATE_REFRESHING || current_Status == STATE_DROP_DOWN) {
                return true;
            }
        }
        return false;
    }

3、頭部的隱藏和顯示操作

//頭部的操作：隱藏，顯示
    class HeadOperation extends AsyncTask<Void, Integer, Integer> {

        @Override
        protected Integer doInBackground(Void... param) {
            int height = params.height;
            //顯示頭部
            if (current_Status == STATE_REFRESHING) {
                while (true) {//讓頭部全部露出來
                    height = height + 50;
                    if (height >= viewHolder_height) {
                        height = viewHolder_height;
                        break;
                    }
                    publishProgress(height);
                    SystemClock.sleep(10);
                }
                //改變狀態：正在重新整理
                current_Status = START_REFRESHING;
                //改變UI更新狀態
                update_ui = true;
                publishProgress(height);
                //重新整理中執行的操作
                if (listener != null) {
                    listener.onRefreshing();
                } else {
                    //預設重新整理時間
                    SystemClock.sleep(5000);
                    //改變狀態：結束重新整理
                    while (true) {
                        height = height - 70;
                        if (height <= 0) {
                            height = 0;
                            break;
                        }
                        publishProgress(height);
                        SystemClock.sleep(10);
                    }
                    current_Status = END_REFRESHING;
                    publishProgress(height);
                    return 1;
                }
            } else if (current_Status == END_REFRESHING) {//隱藏頭部
                while (true) {
                    height = height - 70;
                    if (height <= 0) {
                        height = 0;
                        break;
                    }
                    publishProgress(height);
                    SystemClock.sleep(10);
                }
                publishProgress(height);
                return 1;
            }
            return -1;
        }

        @Override
        protected void onProgressUpdate(Integer... values) {
            params.height = values[0];
            viewHolder.setLayoutParams(params);
            if (current_Status == START_REFRESHING) {
                if (textView != null)
                    textView.setText("正在重新整理。。。。");
            }
        }

        @Override
        protected void onPostExecute(Integer aVoid) {
            if (current_Status == END_REFRESHING) {
                if (listener != null && update_ui) {
                    //重新整理完成後的操作，如提示資訊什麼的
                    listener.onEndRefreshing();
                    update_ui = false;
                }
            }
        }
    }

4、對外的重新整理的介面

 //實現重新整理監聽的方法
    public void setOnRefreshListener(OnRefreshListener listener) {
        this.listener = listener;
    }

    //重新整理的監聽
    public interface OnRefreshListener {
        //正在重新整理：子執行緒
        void onRefreshing();

        //停止重新整理:主執行緒
        void onEndRefreshing();
    }
    //提供一個外部停止重新整理的方法
    public void setEndRefreshing() {
        current_Status = END_REFRESHING;
        new HeadOperation().execute();
    }

5、Activity中

 recyclerView_Refresh.setOnRefreshListener(new RecyclerView_Refresh.OnRefreshListener() {
            @Override
            public void onRefreshing() {//正在重新整理
                SystemClock.sleep(3000);
                //停止重新整理
                recyclerView_Refresh.setEndRefreshing();
            }

            @Override
            public void onEndRefreshing() {//結束重新整理
                Toast.makeText(MainActivity.this, "重新整理完成", Toast.LENGTH_SHORT).show();
            }
        });

需要不同頭部動畫的自行修改，已做註釋；
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